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Arbitrary vars in rule refs #5913

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johanfylling
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@johanfylling johanfylling commented May 10, 2023

This PR adds the possibility to declare rules with variables at arbitrary locations int the ref; e.g.

package example

p[q].r[s] := 42 { q := "foo"; s := "bar" }

By default, the compiler won't allow rule refs to have vars in any other position than the last term; to enable general rule refs, set the OPA_ENABLE_GENERAL_RULE_REFS env var (any value). (is this the best way to do this, or do we have precedence of other ways of setting feature flags?)

Not included in this PR:

  • Feature flag to enable/disable
  • Partial eval
  • Planner implementation
  • Type-checker update
  • Language definition update in docs
  • fmt

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@johanfylling johanfylling force-pushed the jf/5685/multi-var-rule-refs branch 2 times, most recently from 8ef1c96 to 9ae279d Compare May 30, 2023 08:42
@johanfylling johanfylling marked this pull request as ready for review May 30, 2023 11:23
@johanfylling johanfylling changed the title WIP: Arbitrary vars in rule refs Arbitrary vars in rule refs May 30, 2023
ast/compile.go Outdated
@@ -311,6 +335,8 @@ func NewCompiler() *Compiler {
{"BuildComprehensionIndices", "compile_stage_rebuild_comprehension_indices", c.buildComprehensionIndices},
}

_, c.generalRuleRefsEnabled = os.LookupEnv("OPA_ENABLE_GENERAL_RULE_REFS")
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Huh interesting 💡 yeah, why not. We might throw in a _WIP_

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Started looking at it. Still much ground to cover on my side 🔍

ast/index.go Outdated Show resolved Hide resolved
ast/parser.go Outdated Show resolved Hide resolved
test/cases/cases.go Show resolved Hide resolved
topdown/exported_test.go Show resolved Hide resolved
This is the topdown part of supporting generic refs.

Fixes: open-policy-agent#5993

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
@johanfylling johanfylling linked an issue Jun 9, 2023 that may be closed by this pull request
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Sorry it took me so long to get back to this. Some comments and questions inside

ast/parser.go Outdated
@@ -140,6 +142,7 @@ func NewParser() *Parser {
s: &state{},
po: ParserOptions{},
}
_, p.po.generalRuleRefsEnabled = os.LookupEnv("OPA_ENABLE_GENERAL_RULE_REFS")
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💭 treating the environment as a global variable is better avoided, but if we can keep this as a short-term stop-gap, it's probably OK.

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This is temporary, and will be removed once general refs are feature complete. Hopefully soon 🤞. I'm open to improve this if it's too much of an eyesore, though 😅 .

1: true
c:
2: true
# FIXME: Below test case returns: rego_type_error: undefined ref: data.test.p.b
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When? 😅

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This has been solved in the type-checker update I have lined up: johanfylling/opa@jf/5685/multi-var-rule-refs...generic_refs/type-check

#
# p.q[r].s := 1 { r := "foo" }
# p.q[r].s := 2 { r := "bar" }
# query: i := ["foo", "bar"][_]; data.test.p.q[i].s = x
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Maybe quotes help?

Suggested change
# query: i := ["foo", "bar"][_]; data.test.p.q[i].s = x
# query: 'i := ["foo", "bar"][_]; data.test.p.q[i].s = x'

Alternatively, you could query data.test.q and add

q = x {
    i := ["foo", "bar"][_]
    p.q[i].s = x
}

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Hm, looking at this again, I actually get a result with the expected parameters, but with some added "stuff":

{{"$0": 0, "__localq0__": ["foo", "bar"], "i": "foo", "x": 1}, {"$0": 1, "__localq0__": ["foo", "bar"], "i": "bar", "x": 2}}

If I change the query to data.test.p.q[i].s = x, I get a good result:

{{"i": "bar", "x": 2}, {"i": "foo", "x": 1}}

Is this expected, or perhaps an unwanted side effect of my changes 🤔 ? Will try a similar thing on main.

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main exhibit the same behavior. Running opa eval does not output bindings for $0 and __localq0__; so maybe this is a side effect of how the test works?

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Those should never make it out, I think; but opa eval might have some extra code to filter them. Or maybe that was the rego package, https://github.com/open-policy-agent/opa/blob/main/rego/rego.go#L2166-L2168

topdown/eval.go Outdated

func (e *eval) biunifyDynamicRef(pos int, a, b ast.Ref, b1, b2 *bindings, iter unifyIterator) error {
if pos >= len(a) || pos >= len(b) {
return iter()
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So if they don't have the same length, but overlap, we'd accept that?

data.foo.bar = data.foo[x].z

we'd add x = "bar" to the bindings and go on?

But I might be missing something here, I haven't fully understood the topdown change yet.

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We're simply binding any possibly known vars in a rule's ref before evaluating its body.

If data.foo.bar == data.foo.bar.z then I'd expect your snipped should evaluate. (is that even possible, though? 😵‍💫)

This is an interesting case to test for, though; hadn't thought about it from this angle before 🤔.

Perhaps a bit hacky test, but this should trigger this scenario:

package unification

p := i {
    foo.bar.x.y = foo[i].z
}

foo[a][b] := c {
    a := "bar"
    c := {
        "x": {
            "y": 42
        },
        "z": 42
    }[b]
}
$ OPA_ENABLE_GENERAL_RULE_REFS=true opa eval -d . 'data.unification.p'

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Or am I completely misunderstanding you?

// `,
// query: `i := ["foo", "bar"][_]; data.test.p.q[i].s = x`,
// exp: `[{"x": 1}, {"x": 2}]`,
//},
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What's up with these? Do they not work yet; or have they been subsumed by the tests above...? 🤔

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Ah, I missed un-commenting those. Fixed 👍 .

e.e.virtualCache.Put(hint.key, result)
return e.evalTerm(iter, e.pos+1, result, e.bindings)
}

for _, rule := range e.ir.Rules {
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Given that generic ref head rules are the more general case, you might expect that the base case (below) is also covered by what's added above -- is that so? Or what am I missing?

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I think you're right. These two branches should be possible to merge into one; given that there is no performance benefit to keeping them separate.

I think it's around here PE is breaking down too; so I'll dig around here a bit to see what improvements are necessary + possible.

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It's even a bit broken as-is, given that this should be in an elseblock 😅 . I think this rule unification just won't contribute any data in applicable cases, so the result ends up being correct; but we're doing unnecessary work 🤔 .
Scratch that; I'm not even reading my own code right 😄 .

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
…ert()`

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Fixes: open-policy-agent#5994
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
instead of `Or`:ing them

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Nested object created by general ref didn't maintain ground:ness even though containing vars.

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
… with dynamic portion of a rule ref

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
* Adding comments
* Removing unused stuff
* Rename evalOneDynamicRefRulePreUnify() -> evalOneRulePreUnify()

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
…l ref heads

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
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Checked the commits since last week, only had a few questions. It's great to see this progress 🚀

@@ -17,3 +17,26 @@ r[x] if x := 10
p.q.r[x] if x := 10

p.q.r[2] = true

g[h].i[j].k = true
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This looks so wrong but h and j could be rules defined somewhere in the package, right? 😅 (Not that it matters for formatting)

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True, this isn't internally consistent; but it's valid Rego, and for this rule we're more interested to see what the formatter does with the redundant { true } body.

topdown/eval_test.go Show resolved Hide resolved
topdown/eval_test.go Outdated Show resolved Hide resolved
@@ -579,6 +687,7 @@ func TestCheckInferenceRules(t *testing.T) {
t.Fatalf("Unexpected error %v:", err)
}

fmt.Println(env.tree.String())
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Left from testing probably.

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Oops, yea 🤦‍♂️ 😄

Signed-off-by: Johan Fylling <johan.dev@fylling.se>
Signed-off-by: Johan Fylling <johan.dev@fylling.se>
srenatus
srenatus previously approved these changes Aug 31, 2023
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Nitpicks only. Yay, can't wait to get this in. Thanks for the hard work; it's like a summer project 😎

types.NewStaticProperty("c", types.B)},
nil,
expected: types.NewObject(nil,
types.NewDynamicProperty(types.S, types.Any{types.B, types.N, types.S}),
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📝 took me a moment to understand this, but I had overlooked that it's p.q[r].b = 42 and not p.q[r] = 42. So, the extra S keys would (could) be "a", "b", "c". ✔️

Any term, except the very first, in a rule head's reference can be a variable. These variables can be assigned within the rule, just as for any other partial rule, to dynamically construct a nested collection of objects.

{{< danger >}}
General refs in rule heads is an experimental feature, and can be enabled by setting the `OPA_ENABLE_GENERAL_RULE_REFS` environment variable.
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I was wondering about the name for a moment, but I think it's OK. We've got another example here, FWIW.

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Ah, I'll change this to EXPERIMENTAL_GENERAL_RULE_REFS, to align 👍 .

import future.keywords

# A partial object rule that converts a list of users to a mapping by "role" and then "id".
users_by_role[role][id] := user {
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Let's throw in an if here and below

@johanfylling johanfylling merged commit 0431567 into open-policy-agent:main Aug 31, 2023
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general ref heads: topdown
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